This invention relates to a vacuum-type circuit breaker and, more particularly, to means for limiting overtravel of the movable contact of such a circuit breaker at the end of an opening stroke.
The invention also relates to means for dissipating the kinetic energy remaining in the parts of a circuit breaker at the end of a closing operating. This energydissipating feature is usable in other types of circuit breakers as well as the vacuum-type circuit breaker.
The usual vacuum-circuit breaker comprises a contact wipe mechanism between the movable contact of the circuit breaker and the operating linkage for the contacts. This wipe mechanism serves to provide a desired hold-closed force on the contacts despite contact-wear and also to provide for an impact to the movable contact at the start of an opening operation. This wipe mechanism typically comprises a preloaded spring which is further loaded by wipe travel of the operating linkage at the end of the closing stroke after the contacts have engaged. The presence of this wipe mechanism introduces certain problems with respect to termination of an opening stroke. Such problems will be apparent from the following discussion.
More specifically, it is conventional practice to provide an opening dashpot which acts to smoothly and gradually terminate opening motion of the circuit-breaker operating linkage after it has driven the movable contact through an opening stroke. This dashpot is usually designed in such a way that it can terminate opening motion with deceleration forces that are limited to a value less than the preload in the wipe spring, and this relationship prevents the movable contact from overrunning the operating linkage when opening motion of the operating linkage is terminated. But if, for any reason, the opening dashpot should fail, the above-described overrunning of the movable contact can occur, and this can result in significant overtravel and resultant damage to the usual bellows of the vacuum interrupter present in the circuit breaker.
Consideration has been given to overcoming this overrunning problem by providing a stop between the relatively movable parts of the wipe mechanism that acts to block contact overtravel at the end of the opening stroke. But this approach is not feasible in the usual wipe mechanism since such a stop would interfere with the essential overtravel needed at the end of the closing stroke for wipe action.
Another possible way of overcoming the above-described overrunning problem is to provide an opening stop for the movable contact fixed to a stationary frame of the circuit breaker. Such a stop requires cumbersome support structure; and in the circuit breaker I am concerned with, there is no space available for such support structure.